import { Data, Effect } from "effect"
import { parseDocument, stringify, visit } from "yaml"

class FrontmatterParseError extends Data.TaggedError("FrontmatterParseError")<{
	readonly path: string
	readonly message: string
	readonly cause?: unknown
}> {}

interface ParsedFrontmatter {
	readonly data: unknown
	readonly body: string
}

export const parseFrontmatterSync = (
	content: string,
	path: string,
): ParsedFrontmatter => {
	try {
		const match = content.match(/^---\r?\n([\s\S]*?)\r?\n---(?:\r?\n|$)/)
		if (!match) {
			throw new Error("Markdown file must begin with YAML frontmatter")
		}

		const document = parseDocument(match[1]!, {
			customTags: [],
			merge: false,
			schema: "core",
			strict: true,
			uniqueKeys: true,
			version: "1.2",
		})

		const parseMessages = [...document.errors, ...document.warnings]
		if (parseMessages.length > 0) {
			throw new Error(parseMessages.map((error) => error.message).join("; "))
		}

		let unsupportedFeature: string | null = null
		visit(document, {
			Alias: () => {
				unsupportedFeature = "YAML aliases are not supported"
			},
			Node: (_key, node) => {
				if (node.anchor) {
					unsupportedFeature = "YAML anchors are not supported"
				} else if (node.tag && !node.tag.startsWith("tag:yaml.org,2002:")) {
					unsupportedFeature = "Custom YAML tags are not supported"
				}
			},
		})

		if (unsupportedFeature) {
			throw new Error(unsupportedFeature)
		}

		const data = document.toJS({ maxAliasCount: 0 })
		if (data === null || typeof data !== "object" || Array.isArray(data)) {
			throw new Error("YAML frontmatter must be a mapping")
		}

		return {
			data,
			body: content.slice(match[0].length),
		}
	} catch (cause) {
		throw new FrontmatterParseError({
			path,
			message:
				cause instanceof Error ? cause.message : "Failed to parse frontmatter",
			cause,
		})
	}
}

export const parseFrontmatter = (content: string, path: string) =>
	Effect.try({
		try: () => parseFrontmatterSync(content, path),
		catch: (error) => error as FrontmatterParseError,
	})

export const formatMarkdownDocument = (data: object, body: string) =>
	`---\n${stringify(data, { lineWidth: 0 }).trimEnd()}\n---\n\n${body.trim()}\n`

export const formatWorkDocumentBody = (
	title: string,
	kind: "epic" | "task" | "phase",
	purpose?: "investigation" | "implementation",
) =>
	purpose === "investigation"
		? `# ${title}

## Investigation Boundary

State the question, scope, and implementation excluded from this investigation.

## Evidence

Record inspected sources, commands, observations, and supporting links.

## Findings

Record findings, confidence, uncertainty, and relevant constraints.

## Recommendation

Recommend implementation, no change, or further investigation.

## Implementation Handoff

Record any distinct implementation task created from this investigation.

## Important Decisions

Record consequential decisions and their rationale.`
		: `# ${title}

## Outcome

Describe the ${kind} outcome.

## Plan

Describe the current approach.

## Important Decisions

Record consequential decisions and their rationale.`